Full Size M&P 1.0 9mm.
If there was ever a justified need for a high capacity handgun, the “Go To War” specification of this thread is it. I have Taran Tactical +6 extensions on three magazines, giving a load-out of 70 rounds. Barnes TAC-X 115 grn solid copper hollow points.
A GTW handgun is not the typical CCW “self defense” gun or situation. It might be a last ditch effort to save yourself from multiple adversaries; a pro-active, conveniently small, close-range attack weapon with numerous targets; or a keep-their-heads-down-with-numerous-rounds-while-maneuvering or covering fire handgun.
In none of these scenarios would I want to run out of ammo and have to reload (especially a revolver) after 6-9 rounds when I can have 24 rounds on board to start and a fast reload to get another 23 rounds ready.
Prepare for the worst, and take advantage of anything less without compromise. If it only takes a few rounds to solve a problem, so be it. I do not count on or prepare for things to be only that simple.